SQL> desc test;
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- ------------------------------------
 TRANSACTION_ID                                                 VARCHAR2(20)
 NAME                                                           VARCHAR2(20)

SQL> select * from test;

no rows selected

SQL> select seqa.nextval from dual;

   NEXTVAL
----------
        25

LOAD DATA
INFILE *
INTO TABLE test
REPLACE
FIELDS TERMINATED BY ','
TRAILING NULLCOLS
(name char,
 transaction_id " 'auto-' || seqa.nextval"
)

begindata
intel
amd

SQL> $sqlldr scott/tiger@ora10 control=test2.ctl log=test2.log

SQL*Loader: Release 11.2.0.2.0 - Production on Pet Svi 18 12:58:49 2012

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

Commit point reached - logical record count 1
Commit point reached - logical record count 2

SQL> select * from test;

TRANSACTION_ID       NAME
-------------------- --------------------
auto-26              intel
auto-27              amd

SQL>